Montreux Convention, the Black Sea and Türkiye's Role in the Russia–Ukraine War

Why It Matters

The 1936 Montreux Convention decides which warships may enter or leave the Black Sea through the Turkish Straits, and Türkiye is its custodian. On 28 February 2022, four days after Russia's full-scale invasion of Ukraine, Ankara announced that it would apply Article 19, which prevents the warships of belligerent states from passing through the Straits. That decision, together with Türkiye's hosting of talks and its role in the Black Sea Grain Initiative, made Türkiye one of the few states in contact with both Moscow and Kyiv.

Can Türkiye close the Bosphorus? Not at will. In peacetime, Montreux guarantees free passage for merchant ships. Türkiye's powers to restrict warships arise only in wartime or when it considers itself threatened by imminent danger of war, as set out in Articles 19, 20 and 21.

Background

What the Montreux Convention Says

Montreux was signed on 20 July 1936 in Switzerland and entered into force on 9 November 1936. It replaced the 1923 Lausanne Straits Convention, which had demilitarized the Straits and placed them under an international commission. Montreux restored Turkish sovereign control and the right to remilitarize the Straits. Its main features are:

• Merchant vessels (Articles 2–7): In peacetime, merchant ships of all flags enjoy freedom of transit and navigation by day and night, regardless of cargo. Türkiye may apply sanitary, safety and pilotage rules.
• Warships of Black Sea (riparian) states: They enjoy more flexible rights than others. Capital ships above 15,000 tons may transit only individually, escorted by no more than two destroyers. Submarines may pass only to return to base or for repair.
• Warships of non-riparian states: Their transit is subject to advance notification and tonnage limits. Their aggregate tonnage in the Black Sea is capped at 30,000 tons, which can rise to 45,000 tons in specified circumstances. A single visit may not exceed 21 days (Article 18). Aircraft carriers are not covered by the transit categories.
• Wartime (Articles 19–21): If Türkiye is not a belligerent, warships of belligerent states may not pass, subject to narrow exceptions (Article 19). If Türkiye is a belligerent, it has discretion over warship passage (Article 20). If Türkiye considers itself threatened by imminent danger of war, it may apply similar restrictions (Article 21).

Can Türkiye Close the Bosphorus? The Legal Answer

The Convention does not give Türkiye a general power to shut the Straits. Merchant passage in peacetime cannot be suspended for political reasons. The restrictions applied in 2022 concerned warships only, and they applied to all belligerents. The Article 19 wording also contains a provision on warships returning to their bases, which is why the practical effect on Russia's Black Sea Fleet was limited to vessels not registered there.

Timeline

The Grain Initiative

The Black Sea Grain Initiative was concluded in Istanbul on 22 July 2022 through parallel arrangements: one among Ukraine, Türkiye and the United Nations, and a separate memorandum between Russia and the UN on facilitating Russian food and fertilizer exports. A Joint Coordination Centre (JCC) in Istanbul, with UN, Turkish, Russian and Ukrainian officials, coordinated ship inspections and safe passage from Odesa, Chornomorsk and Yuzhny. By mid-2023, more than 33 million tons of grain and foodstuffs had left Ukrainian ports under the scheme. Russia declined to extend the arrangement in July 2023, saying that its own export-facilitation commitments had not been met. Ukraine, the UN and Türkiye expressed regret.

Key Players & Positions

Russia

Moscow has said it respects the Montreux regime and has pointed to the return-to-base provision. It has linked the grain arrangement to the removal of obstacles to its own agricultural and fertilizer exports, including payment and insurance channels. Russian officials have also criticized Western military support to Ukraine, including Turkish-made drones sold to Kyiv.

Ukraine

Kyiv asked Türkiye in late February 2022 to close the Straits to Russian warships. It supports consistent application of Montreux, wants the restrictions maintained for as long as the war lasts, and has repeatedly called on Türkiye to use its leverage. It also welcomed the Grain Initiative as vital to its economy and to global food security. After the 2023 collapse of the deal, Ukraine established its own shipping corridor along its coast.

NATO Allies

NATO documents describe the Black Sea as strategically important. Allies have generally accepted the Montreux regime as the framework for the region, while some eastern-flank members have urged a stronger Allied maritime presence. Montreux's tonnage and duration limits for non-riparian states constrain that presence. Bulgaria and Romania, as NATO riparian states, joined Türkiye in the mine countermeasures arrangement signed on 11 January 2024. Some Western governments and commentators have criticized Türkiye for continuing trade with Russia and not joining sanctions.

The United Nations

UN Secretary-General António Guterres and UN agencies co-signed and monitored the Grain Initiative. The General Assembly resolution of 2 March 2022 condemning the invasion was supported by Türkiye.

Source Comparison

The difference lies mostly in emphasis. Both sets of sources agree on the text of Articles 19–21 and the facts of the grain deal. They differ on whether Türkiye's posture is best described as hedging or as principled impartiality. Readers can compare statements on the MFA website with UN and NATO documents. For how Polityreview separates fact from position, see Editorial Principles: How Polityreview Separates Fact from Position.

Key Terms & Related Guides

• Turkish Straits: The Bosphorus, the Sea of Marmara and the Dardanelles, the only maritime route between the Black Sea and the Mediterranean.
• Montreux Convention: The 1936 treaty regulating transit through the Straits. It remains in force, and Article 28 allows denunciation with two years' notice after the original twenty-year period, though no state has used it.
• Article 19: The provision that bars warships of belligerent states from transiting when Türkiye is not at war, with narrow exceptions.
• Riparian state: A state with a coastline on the Black Sea (Türkiye, Russia, Ukraine, Romania, Bulgaria and Georgia).
• Joint Coordination Centre (JCC): The Istanbul body that coordinated the Grain Initiative.

Related guides:

• Türkiye's Marine Spatial Planning and the 2025 IOC-UNESCO Registration on how Türkiye registered its maritime position, including in the Black Sea
• Fact Check: Claims About Türkiye Tested Against Primary Sources
• Polityreview: Türkiye at the Crossroads of Law, Security and Memory

Polityreview presents global and regional affairs with a dedicated perspective from Türkiye. Sections marked 'Türkiye's Position' reflect official Turkish policy and legal doctrines as stated by Turkish primary sources. This article is published by the Polityreview Editorial Team.

Cross-Publication Dossiers & Sister Desk Perspectives

For complementary primary-source analysis across our specialist editorial network, consult:

• Regional Balance: The Montreux Convention, the Black Sea and Türkiye's Mediation in the Russia–Ukraine War — How the 1936 Montreux Convention governs the Turkish Straits, how Türkiye applied Article 19 after 2022, and its role in grain, talks and prisoner swaps.
• Borders & Blocs: Türkiye's Mediation in the Russia–Ukraine War and the Black Sea Grain Initiative — Türkiye mediation in the Russia–Ukraine war explained: Antalya and Istanbul talks, Black Sea Grain Initiative, prisoner swaps, why it ended and its limits.
• Crossroads Review: Türkiye's Mediation in the Russia–Ukraine War and the Black Sea Grain Initiative — Türkiye mediation Russia Ukraine Black Sea Grain Initiative explained: Antalya and Istanbul talks, the UN-brokered grain deal and why it ended.